Size-tunable, hexagonal plate-like Cu ₃P and Janus-like Cu-Cu ₃P nanocrystals

We describe two synthesis approaches to colloidal Cu ₃P nanocrystals using trioctylphosphine (TOP) as phosphorus precursor. One approach is based on the homogeneous nucleation of small Cu ₃P nanocrystals with hexagonal plate-like morphology and with sizes that can be tuned from 5 to 50 nm depending on the reaction time. In the other approach, metallic Cu nanocrystals are nucleated first and then they are progressively phosphorized to Cu ₃P. In this case, intermediate Janus-like dimeric nanoparticles can be isolated, which are made of two domains of different materials, Cu and Cu ₃P, sharing a flat epitaxial interface. The Janus-like nanoparticles can be transformed back to single-crystalline copper particles if they are annealed at high temperature under high vacuum conditions, which makes them an interesting source of phosphorus. The features of the Cu-Cu ₃P Janus-like nanoparticles are compared with those of the striped microstructure discovered more than two decades ago in the rapidly quenched Cu-Cu ₃P eutectic of the Cu-P alloy, suggesting that other alloy/eutectic systems that display similar behavior might give origin to nanostructures with flat, epitaxial interface between domains of two diverse materials. Finally, the electrochemical properties of the copper phosphide plates are studied, and they are found to be capable of undergoing lithiation/delithiation through a displacement reaction, while the Janus-like Cu-Cu ₃P particles do not display an electrochemical behavior that would make them suitable for applications in batteries.